The present invention relates to a method for making an air filter. More specifically, a non-woven fabric mat of fibers and a net of synthetic resin having different tacifying temperatures are thermobonded to form the filter. The invention further relates to an improved filter causing little air pressure loss and having high form stability.
A conventional air filter such as would be used in air conditioners, coolers, heating apparatus, ventilation devices, air cleaners and the like is usually composed of nets woven from polypropylene fibers, salane fibers and the like or rough non-woven fabrics. Manufacturing such filters requires sewing the edge portions of the nets or rough non-woven fabrics or requires joining their edges by injection bonding means in order to prevent the edge portions from becoming frayed. While this is necessary because the nets or rough non-woven fabrics used have reduced mechanical strength and lower form stability, it also leads to a high cost of production.
Air filters have also been produced by joining nets having high form stability with non-woven fabric mats. The operation for joining these nets with the non-woven fabrics however, is remarkably troublesome. Substantially uniform bonding is not attained and the fabric can separate from the net when contacted by forced air. In addition, such a filter is less desirable in that use of the net having higher form stability leads to a decrease in the ventilating property of the filter and an increase in pressure loss across the filter.